The present invention relates in general to the relief of asymmetrical stresses in fibre optic arrays, and in particular to the relief of asymmetrical stresses on polarizing (PZ) or polarization-maintaining (PM) fibres supported in grooved assemblies.
Polarization maintaining (PM) fibres are fibres that have been especially developed to maintain polarization of light polarized along one of the principal axes of polarization of the fibre and transmitted therealong under adverse conditions. With such fibres, light polarized along one of the principal axes travels at a different rate than light polarized orthogonal to that axis. In particular, PM fibres will maintain polarization under most stresses applied externally to the fibre in use. For example, a one metre long connectorized patchcord constructed with PM fibre can maintain polarization to at least 30 dB at a wavelength of 1550 nm. The polarization-extinction ratio of PM fibres can be degraded by microbending or by stresses within the connectors used or by external optical components that do not maintain polarization properly. Special termination procedures, low stress glues, and top quality lenses and optics must be used to minimize stresses introduced into the PM fibres so as to achieve and maintain high extinction ratios.
One common type of connector that can make use of PM fibres is a v-groove assembly in which one or more PM fibres are arranged side-by-side, with each fibre located in its own v-groove of a substrate member. Typically, although not always, a cover plate is positioned over the array of fibres and a low stress glue or potting compound compatible with the fibres and the substrate is provided, with the glue or potting compound surrounding or encapsulating the fibres and substantially filling in most voids therearound. After the glue or potting compound has cured and the end face has been prepared the assembly is ready for use.
One problem with v-groove assemblies has been noted, that being the fact that the outboard or curb fibres of each array within the assembly appear to exhibit somewhat degraded extinction ratios in comparison to any remaining inboard fibres, namely those between the two curb fibres. It would appear that such inboard fibres all have a substantially symmetrical surrounding volume of glue or potting compound whereas curb fibres have an asymmetrical surrounding volume of glue or potting compound. This is the result of the flow properties of the glue or potting compound when it is applied and then cured, the glue or potting compound not being constrained adjacent to curb fibres to the same extent as it is between those curb fibres. The asymmetrical constraint results in an asymmetrical distribution of the forces within the glue or potting compound and this in turn affects the distribution of stresses to which the fibres are subjected.